Apple unveiled the next iteration of the iPhone operating system today, and while there will be over 100 changes to the system, there were seven new features that they felt were important enough to call them “tentpoles.”

Steve Jobs took to the stage today to walk everyone through the seven most important new features of the iPhone OS 4, although we would debate one of those as being “important.” They include:

Multitasking
Folders
Unified Inbox
iBooks
Enterprise
Game Kit
iAd
All told there are over 100 user features, and over 1500 new developer APIs in the new version of the operating system. A quick break down of each:

Multitasking: Possibly the most requested feature of the OS for a long time now, it will do just what you think it will be allowing you to run things like the Pandora app in the background so you can have music playing while you do other tasks.

Folders: You will now be able to group apps into folders, this will increase the number of apps from 180 to over 2,000 that you can have on the device. Click on a “Games” folder, and you will be in a separate set of screens just for the apps you placed there.

Unified Inbox: You will now be able to see all of your various inboxes in one window so you won’t have to flip back and forth, and you will also be able to have more than one Exchange account. As an even bigger bonus, you will now be able to thread e-mails. Attachments will now be able to open in apps.

iBooks: This was the one thing that even Steve Jobs seemed a bit indifferent to, but you can sync your reading between the various Apple devices running this app.

Enterprise: Enterprise users will be able to do over the air updates of apps off of their own servers, and there will be increased security.

Game Kit: A social network of gaming is coming that will include leaderboards and achievements.

iAd: A new advertising platform that is built right into the OS and provide a much richer ad experience that will almost be like an app inside of the app. There will be games, downloads, opportunities to see other apps and developers will get 60% of the revenue.

The new version of the OS will be available for the iPhone 3G S and iPod Touch 3rd generation this summer, iPhone 3G and iPod Touch 2nd generation users will get it also, but won’t be able to use some features such as multitasking. The iPad will receive the update in the fall.